1. Field of the Invention
The present invention relates to a developing roller in a developing device to be used in an image forming apparatus, such as a copying machine, a facsimile and a printer. More particularly, the invention relates to a developing sleeve wherein an amount of a developer on a surface of the developing sleeve is uniform without imposing a stress on the developer by a regulating member.
2. Discussion of the Background
A developing roller in a developing device used in an image forming apparatus, such as a copying machine, a facsimile, a printer, and so forth generally includes a developing sleeve and a magnet. A developer is carried on a surface of the developing sleeve and conveyed to develop a latent image formed on a surface of a photoconductive element into a visible image. If an amount of the developer on the surface of the developing sleeve is not uniform, the developed visible image has an uneven image density, resulting in a degradation of a produced image. Therefore, it is preferable that the amount of the developer on the surface of the developing sleeve is uniform. In order to keep the amount of the developer on the surface of the developing sleeve uniform, a regulating member, which is referred to as a doctor, is generally employed.
The amount of the developer in end portions of the developing sleeve is increased compared to that of the developer in a central portion of the developing sleeve because of a wraparound magnetic force generated by an end portion of a magnet. Thus, the amount of the developer is locally increased in the vicinity of the end portion of the magnet, resulting in a coagulation of the developer on the surface of the developing sleeve due to a stress imposed on the developer.
In Japanese Patent Laid-Open Publication No. 9-265238, a technology for reducing an amount of a developer in the vicinity of a magnet by changing a magnetic force exerted on the doctor or a shape of the doctor to increase a regulating force of the doctor. In the above-described technology, the developer which passes the doctor undergoes a stress. Thus, a strain results on the developer. The developer which undergoes the stress tends to move to a portion of the developing sleeve where a reduced stress is imposed on the developer.
If there is strain on the developer, a property of the developer may change, resulting in an early deterioration of the developer. In addition, when the developer moves to the portion of the developing sleeve where a reduced stress is imposed on the developer, an amount of the developer increases locally at this portion of the developing sleeve, resulting in the coagulation of the developer. In addition, the developer scatters when the developer undergoes a stress imposed by the regulating member.
The present invention has been made in view of the above-mentioned and other problems and addresses the above-discussed and other problems.
The present invention advantageously provides a novel developing roller, developing device using the developing roller, and image forming apparatus using the developing device, wherein a developer on a developing sleeve is uniformed without imposing a stress on the developer by a regulating member, thereby a coagulation of the developer on the developing sleeve is prevented. In addition, a scattering of the developer, an early deterioration of the developer, and a deterioration of a sealing member by the developing sleeve are prevented.
According to an example of the present invention, the developing roller includes a magnet roller including a plurality of magnets configured to attract the developer, and a developing sleeve provided outside of the magnet roller and configured to carry and convey the developer while bearing the developer by a magnetic force of the magnet roller. The surface of the developing sleeve is configured such that a transportation capacity of the developer in end portions of the developing sleeve which correspond to a vicinity of ends of the magnet roller is smaller than the transportation capacity of the developer in a central portion of the developing sleeve which corresponds to a central portion of the magnet roller.